The hard lines were all replaced during the restoration. But it doesn't mean they're holding fluid. The car is still up on the lift so I'll check the fittings each day.I suspect the fittings on the lines. The ones from my master cylinder are originals from a 73-76 front disc A body car so they are maybe 50 years old. The threads do get worn after multiple on/off sessions.
If your fittings are "seasoned", your problem may lie there.